Polyesters and copolyesters are useful materials for injection molding and extrusion, but their heat deflection temperatures are often relatively low. Polyetherimides are plastics with excellent flexural strength and performance at high temperature; however high temperature are generally required to process them. Polyetherimides are also generally more expensive than polyesters. Blending polyesters with polyetherimides could provide compositions that have satisfactorily high heat deflection temperatures together with processing temperatures lower than those required for pure polyetherimides. Further, economical blends having good flexural strength would be desirable for certain uses.
Blends of polyesters and polyetherimides are disclosed in U.S. Pat. No. 4,141,927. Polyesters of terephthalic acid and isophthalic acid with ethylene glycol are disclosed. Cyclohexanediol is mentioned as a possible glycol but there is no suggestion of cyclohexane-1,4-dimethanol. No mention is made of blends having high heat deflection temperatures and low processing temperatures.
Blends of polyarylates with polyetherimides are disclosed in U.S. Pat. Nos. 4,250,279 and 4,908,419. Three component blends of polyetherimide, polyester, and another polymer are also disclosed in U.S. Pat. Nos. 4,687,819 and 4,908,418. U.S. Pat. No. 4,908,418 mentions a polyester of 1,4-cyclohexanedimethanol as a suitable polyester for the three-component blend. In none of these references is there a suggestion of a polymer blend having the properties of high heat deflection temperature and low melt processing temperature.
The present invention provides novel thermoplastic blends of polyetherimides and copolyesters that have in combination a lower processing temperature than the polyetherimide, a desirably high heat deflection temperature and a high flexural modulus. In addition, certain compositions of the invention form single phase solid solutions of excellent clarity. These compositions are especially useful for forming clear molded articles having good high temperature properties.